For a long time it has been a practice to form annular articles, such as rims for steering wheels, gears, and the like, of laminations of a non-flowable strength-giving base material and a flowable hardenable bonding material. Where great strength is not a material consideration, paper has been used as the base material; where greater strength is desired, woven fabric or other strong materials have been used as the base material. Conveniently, it has been usual to impregnate the base material with the bonding material before the laminating elements are formed, as by die-cutting. A bonding material now commonly used, when the parts need to be hard, rigid, and serviceable, is a phenolic condensation product.
An important consideration in producing laminated annular articles is to produce laminae blanks from sheet material and to do so with the minimum amount of scrap, sometimes referred to as drop off. The most convenient form of sheet to use in production is a strip, ribbon or tape taken from a large roll.
U.S. Pat. No. 1,315,896, Sept. 9, 1919, offers one example of a proposal to conserve sheet material when cutting lamination elements or blank segments for making gear annuli to avoid having to cut complete annuli from a sheet, the segment ends being cut on radii of the annulus to be formed; but it can be seen that with this proposal the percentage of scrap is very great as compared with the useful segmental blanks produced.
U.S. Pat. No. 935,826, Oct. 5, 1909, offers another example of a proposal to get the maximum number of blanks from a strip of material fed off a roll; but here, again, the percentage of scrap is very considerable. Incidently the blanks are used for forming frusto-conical cups and the situation is not closely comparable to the production of blanks to form laminae of annular particles.
The next major consideration is to form the annulus of laminations but without voids in the base material. This, of course, is possible by forming the blanks with ends matching radii of the annular article to be made, as in the patent referred to above; but obviously, this entails much scrap loss from the sheet, especially if it is desired that the blanks be cut from a strip or tape with parallel sides and conveniently fairly narrow, as supplied from a roll for rapid production. When an article with voids in the base material is finished under heat and pressure the bonding material will flow into and fill the voids but the void fillings will have less strength than if the base material had been present, and this is particularly objectionable where gear teeth are cut in the periphery and the greatest possible homogeneity and strength are desired.
Another consideration is the manner in which blank segments are deposited in an annular container form, bucket, or cup in the lay-up stage. They must be disposed flatwise, evenly and preferably end-abutting when segmental blanks are used. This and the factor of desired speed practically eliminate consideration of preforming and hand-layup. Hence, there is a preference for cutting and depositing blanks directly into the assembly container. And since any scrap formed is likely to fall into a container to produce inferior and possibly discardable articles, any scrap or trimming at this stage is undesirable.
As to apparatus, one prior practice has been to bring a plurality of sheets from rolls into stacked relationship at a press; punch out arcuate laminar segments of practically full strip width into an annular rotatable bucket against an annular spring-supported bottom ring, the segments being placed end-to-end in each layer and end-staggered like brickwork in adjacent layers; bringing a clamp ring down on a completed annular blank and clamping it to the bottom ring; then removing the clamped blanks to an oven and consolidating them by heat. The clamps are re-used in taking other blanks from the buckets, the bottom rings being put back in the buckets. The forming machine has a plurality of rotatable buckets which are brought successively into blank-punching position for filling. The punch-die unit cuts an arcuate segment on both ends and on at least one arcuate side so there is drop-off which is blown away. The drop-off is used, if possible, for inferior parts which can use small-sized material; if not, it is lost as scrap. And since the material is quite expensive it is desirable to minimize or eliminate drop-off or scrap. Also it is desirable to avoid or minimize hand operations involved in this prior practice.